Differentiation of semantic dementia and Alzheimer's disease using the Addenbrooke's Cognitive Examination (ACE)

Abstract

The Addenbrooke's Cognitive Examination (ACE) is a simple diagnostic tool bridging the gap between the very brief Mini Mental State Exam (MMSE) and much longer test batteries used by neuropsychologists which has proven extremely popular internationally. We aimed to assess the ability of the ACE to differentiate semantic dementia (SD) from Alzheimer's disease (AD). The ACE was administered to three groups: SD patients (n = 40) and two separate groups of AD patients (n = 40 in each), matched for overall ACE or MMSE score. Significant differences were found between SD and both AD groups for the ACE sub-scores of naming, reading and orientation in time. Discriminant analysis (SD versus AD) led to the formulation of a 'semantic index' (naming plus reading minus scores for serial-7s, orientation in time and drawing). Application of the semantic index to the patient data found values of less than zero to be predictive of SD rather than AD with 88% sensitivity and 90% specificity. Validation analysis in an independent sample of 24 SD and AD patients proved even more favourable. The overall ACE score is known to be a sensitive, and specific, indicator of early neurodegenerative dementia; this study shows that the ACE can also be used to detect SD through application of the semantic index.